1. Field of the Invention
The present invention relates to a photoelectric conversion device and, more particularly, to a photoelectric conversion device in which common read lines are connected in a matrix.
2. Related Background Art
A conventional photoelectric conversion device used in an image reading apparatus such as a facsimile machine comprises a plurality of blocks each including a plurality of sensor elements each including a combination of a photoelectric conversion section, a charge storage section connected to the photoelectric conversion section, and a switch section arranged in a path for reading out a charge from the charge storage section. That is, since a photoelectric conversion device of this type has small photoelectric conversion sections linearly arranged at a high density, the sensor elements are grouped into blocks and wired in a matrix in units of blocks by using common read lines connected to the switch section.
FIG. 1 is a block diagram showing a basic arrangement of a conventional photoelectric conversion device of the type described above.
Referring to FIG. 1, a sensor section consists of blocks 2-1 to 2-n. Each block contains m sensor elements each consisting of a combination of a photoelectric conversion section, a charge storage section, and a switch section. A total number of bits of this photoelectric conversion device is n.times.m. A power source 4 applies a common voltage to the photoelectric conversion sections of all the blocks. A drive circuit 1 sequentially drives all the blocks. Wiring lines 6 connect the drive circuit 1 to the switch sections of the blocks. A read circuit 3 extracts a common output from the photoelectric conversion sections corresponding to each block. Wiring lines 5 connect the switch sections of the blocks to the read circuit 3. Shield wiring lines 7 are connected between the wiring lines 5 and are grounded.
FIG. 2 is a circuit diagram showing one of the blocks described above.
Referring to FIG. 2, each block includes photoelectric conversion sections 13, charge storage sections 14, reset switch sections 15, and transfer switch sections 16. A combination of the photoelectric conversion section 13, the charge storage section 14, the reset switch section 15, and the transfer switch section 16 constitutes one sensor element. In this case, each block consists of sensor elements 11-1 to 11-m.
FIG. 3 is a wiring pattern diagram showing a detailed arrangement of the photoelectric conversion device. In this case, each block consists of two sensor elements, and the photoelectric conversion device consists of two blocks. For illustrative convenience, FIG. 3 shows only upper and lower wiring patterns and contact holes.
More specifically, a block 11 consists of sensor elements 11-1 and 11-2, and a block 12 adjacent to the block 11 consists of sensor elements 12-1 and 12-2. The elements represented by reference numerals 13, 14, 15, and 16 are defined as described with reference to FIG. 2.
A wiring line 21 connects a power source 4 to one electrode of each of the photoelectric conversion sections 13 of all the blocks. A wiring line 22 connects the power source 4 to one electrode of each of the charge storage sections of all the blocks and is grounded. A discharge wiring line 23 is connected to the reset switch sections 15 of all the blocks.
The gate lines of the transfer switch sections 16 of the two sensor elements 11-1 and 11-2 in the block 11 are commonly connected to a wiring line 31. The gate lines of the reset switch sections 15 of the two sensor elements 11-1 and 11-2 are commonly connected to a wiring line 32. Similarly, the gate lines of the transfer switch sections 16 of the two sensor elements 12-1 and 12-2 in the block 12 are commonly connected to the wiring line 32. The gate lines of the reset switch sections 15 of the two sensor elements 12-1 and 12-2 are commonly connected to a wiring line 33.
The read line from the transfer switch section 16 of the sensor element 11-1 in the block 11 and the read line from the transfer switch section 16 of the sensor element 12-1 in the block 12 are commonly connected to a wiring line 34. Similarly, the read line from the transfer switch section 16 of the sensor element 11-2 in the block 11 and the read line from the transfer switch section 16 of the sensor element 12-2 in the block 12 are commonly connected to a wiring line 35, thereby forming a wiring matrix.
Shield wiring lines 36, 37, and 38 are grounded. The shield wiring lines 36, 37, and 38 have a function of eliminating capacitive coupling of the common read wiring lines 34 and 35 and preventing crosstalk of the read signals.
Since the conventional photoelectric conversion device described above, however, has the shield wiring lines, the width (i.e., a width in the vertical direction in FIG. 3) of a wiring section including the common gate wiring lines, the common read wiring lines, and the shield wiring lines is increased. Assume that an A4 sized original is read at a resolution of 8 lines/mm, that the number of bits per block is 42, and that the photoelectric conversion device has 42 blocks. Under these assumptions, the wiring section must consist of 42 common read lines, 43 shield wiring lines, and 43 common gate wiring lines. When these wiring lines are formed by a 10-.mu.m line and space rule, a total width becomes 2,570 .mu.m, and the photoelectric conversion device becomes a large scale one. Since a number of photoelectric conversion device chips available from a substrate is greatly reduced, greater producing cost would be incurred. In addition, since a large number of wiring lines are formed, manufacturing yield is decreased.